The introduction of flowable material to an implantation site within a patient to effect one or more therapeutic goals is well known. The flowable material itself may be of high or low viscosity. Matter ranging from typical fluids or solutions to non-Newtonian fluids, pastes, gels and the like has been used for one purpose or another in the medical arts.
It is well-recognized that syringes may be used for percutaneous delivery or injection of flowable material. However, such devices are of limited value in the delivery of high viscosity fluids. In general, users are only capable of generating pressures of about 100-150 psi with 10 cc syringes. This places a limitation on the viscosity of the flowable material that can be effectively “pushed through” the syringe and attached needle or cannula and fully delivered to a treatment site. The use of a small barrel syringe, e.g., a 1 cc syringe enables the user to generate higher driving pressures (e.g., pressures of 800 psi and possibly as high as 1000-1200 psi) that may be used to flow a viscous implant material. However, the 1 cc volume of the syringe may be very limiting as to the amount of material deliverable to a patient. This can be especially problematic when the material to be injected is a settable composition where (for various reasons) it is important to deliver all the material desired in a single “shot”. Another problem with a 1 cc syringe is lack of control, as high pressures are generated in a “spike-like” response time and are not continuously controllable.
Other devices used in the medical arts do not suffer such a control problem by virtue of a threaded arrangement used to advance a piston head within a bore to drive material from a loaded device. U.S. Pat. No. 29,083 to Irving discloses a syringe having a plunger with a screw thread on its exterior. Advancing the plunger by turning it relative to a housing generates sufficient pressure to force a semi-solid ointment out of a perforated tube. This applicator, however, is only configured for rectal delivery of a hemorrhoid medicament.
By contrast, U.S. patent application Ser. No. 09/053,108, “Pressure Applicator for Hard Tissue Implant Material,” by Preissman, filed Apr. 1, 1998 and U.S. patent application Ser. No. 09/409,934, “High Pressure Applicator” by Preissman, filed on even date herewith, each incorporated by reference herein as part of the invention, disclose high pressure applicators utilizing two threaded columns in various arrangements capable of use for injecting material in useful procedures.
While the applicator of the earlier-filed patent application by Preissman does not provide some of the advantages of the present invention (particularly in loading implant material), the applicators disclosed in each patent application are of practical utility as high-pressure applicators for use in percutaneous vertebroplasty. In this procedure, once a cannula is positioned in the cancellous bone of a vertebrae, a hard tissue implant material such as Polymethylmethacrylate (PMMA) is injected into a site for treatment to reinforce and solidify the damaged hard tissue.
Generally, about 3.5 cc of implant material per side of the vertebral body is required. Control issues aside, this makes the use of a 1 cc syringe problematic. Basically, a vertebroplasty procedure would require multiple reloading steps with such a syringe. Further, the additional time spent for such action would result in more than mere inefficiency. Reloading time is time spent while an implant material like PMMA is polymerizing to become increasingly viscous beyond a state in which it may be safely or effectively delivered by any type of injection device, regardless of its high-pressure capacity. Both the need to inject the implant material through a relatively narrow needle or cannula and the fact that the desired site is relatively closed (i.e., trabecular bone) compounds material thickening effects which make “single shot” delivery ability important.
While PMMA in a nearly-solidified state is inappropriate for use with the present invention, a highly-viscous or syrupy consistency of PMMA is generally believed to be most advantageous for performing percutaneous vertebroplasty. Such a consistency insures that the implant material stays in place much better than a less viscous, more flowable material.
It is known that leakage or seepage of PMMA from a vertebral implant site or extravasation through fractures in the bone can cause a host of complications—some of which can be very serious and even result in death. For example, Weil et al. reported cases of sciatica and difficulty in swallowing which were related to focal cement leakage, Radiology 1996; Vol. 199, No. 1, 241-247. A leak toward the distal veins poses an even more serious risk since this can cause a pulmonary embolism which is often fatal.
In addition to leakage around the cannula and through bone, overfilling of the intended implant site can result in introduction of implant material into the blood stream after removal of the cannula from the implant site. Due to the high pressures involved in the implant procedure, compliance within the delivery system can act as a capacitance under pressure thereby storing a volume of the implant material and energy under pressure which, upon release of the pressure, drives an undesired additional amount of implant material into the implant site to cause potentially-dangerous overfilling. This additional amount of outflow is sometimes referred to as “oozing” or “drip”. System compliance may also result in decreased response performance of the delivery system.
Compliance may be introduced into a system either by virtue of appreciable elasticity of tubing, by other members forming part of the delivery system or by air bubbles introduced in the filling or loading of the applicator with implant material. Purging of air from a system loaded with highly-viscous matter may be difficult or impossible especially where air bubbles are not initially only near the system's outlet. This is because air bubbles will simply not be able to buoy to a point where they may be ejected without extruding a large volume of the implant material intended for implantation from the applicator.
Specific adaptation for venting or purging of air from a syringe for delivering viscous material is disclosed in U.S. Pat. No. 4,795,444 to Hasegawa et al. In this device, space is provided in a top section of the syringe so that an end of a plunger may pass through material in the top section to vent air bubbles before forming a seal in the smaller diameter bottom section of the syringe. The differential in sizes of the sections may be provided in stepwise fashion, as a tapered wall or as by a recessed channel. All this being said, as stated previously—a syringe is of limited utility or practicality as a high pressure applicator and cannot be effectively used as an applicator in the present invention due to various shortcomings inherent to the limitations of syringes as discussed above.
Accordingly, especially for use with PMMA in percutaneous vertebroplasty procedures, there exists a need for an improved system able to provide substantially non-complaint and precise application of implant material under high pressures to a desired location in a single batch. The system of the present invention includes method and apparatus adapted to meet such needs as well as provide other advantages readily apparent to those with skill in the art.